Epimutation ? mitotically stable gene silencing associated with epigenetic alteration in DNA methylation ? is now recognized as a common feature of human cancer. Indeed, recent epigenomic studies revealed that nearly all tumor types harbor hundreds of aberrantly hypermethylated and silenced promoter CpG island- associated (CGI-associated) genes, highlighting the need to identify driver epimutations. In this regard, we developed a novel mouse model of epimutation in a tumor suppressor gene p16 (also known as cyclin- dependent kinase inhibitor 2A). We found that engineered promoter methylation leads to accelerated p16 epimutation in mouse somatic tissues during aging. We demonstrated that p16 epimutation predisposes mice to spontaneous tumor development. In addition, our preliminary work shown that p16 epimutation can cooperate with mutational Apc to accelerate intestinal tumorigenesis using the ApcMin/+ mice. Importantly, we found that p16 epimutation functions beyond the classically known cell-cycle control to induce malignant transformation of intestinal neoplasms. Therefore, based on our strong preliminary data, we hypothesize that p16 epimutation, commonly observed in human sporadic CRCs as part of the age-related epigenetic alteration, cooperates with genetic alterations to drive intestinal cancer initiation and progression. We will test this by 1) Determine how p16 epimutation promotes intestinal tumorigenesis. We will assess the biological consequences of p16 epimutation through its interactions with two key signaling pathways: WNT-APC-?- catenin and MAPK-RAS-RAF; 2) Determine whether reversal of epigenetic defects in p16 suppresses tumor growth. We will evaluate tumor responses to the reversal of p16 epimutation by applying a CRISPR-based targeted p16 promoter demethylation; and 3) Determine whether transcription factors as a reader of methylated DNA mediate the function of p16 epimutation. We will investigate the molecular events by which p16 epigenetic silencing is a result from DNA methylation dependent trans-acting protein binding which subsequently recruits chromatin repressive complexes. These studies will elucidate how aberrant DNA methylation, an important epigenetic mechanism regulating the expression of tumor suppressor genes, drives colorectal tumorigenesis. The results derived from this proposal could have a unique impact in the design of colon cancer epigenetic therapies.
(Relevance Statement) Epigenetics refers to the study of mitotically heritable changes in gene function without accompanying DNA sequence alterations; of the known epigenetic mechanisms, aberration in DNA methylation is a common feature of human cancer. The proposed research is relevant to public health because it will advance our understanding of how aberrant DNA methylation, frequently observed in colon cancer patients, drives cancer development. The proposed project will also contribute significantly to the ongoing search for new and improved strategies of cancer therapy and prevention.